Spare Parts Inventory Strategy for Maintenance Teams

Every maintenance storeroom is a compromise. Stock too little and 1 failed component can stop a line. Stock too much and capital sits on shelves while parts age. A clear inventory strategy turns that compromise into a set of deliberate decisions.

Start with the asset list, not the shelves

Many storerooms grow by accident: leftovers from projects, bulk purchases and items ordered "just in case" after a breakdown. Before deciding what to keep, list the assets the plant depends on and the parts each one uses.

For each machine, collect:

• The bill of materials or spare parts list from the manufacturer
• Nameplate data for motors, pumps, drives and controllers (see how to read a machine nameplate)
• Maintenance history: which parts have failed, how often and with what consequence
• Whether the machine is still supported by its manufacturer

Without this link between assets and parts, the storeroom is just a collection of boxes.

Classify parts by criticality

Not every part deserves the same treatment. A common approach is to rate each part on 2 axes: the consequence of not having it, and how hard it is to get.

Consequence of a stockout

Ask what happens if the part fails and none is available. Does production stop, slow down or continue on a redundant unit? Is there a safety or environmental impact? Many teams use a simple scale such as vital, essential and desirable (often called VED analysis).

Difficulty of supply

Ask how easily the part can be obtained. A standard deep groove ball bearing is usually available from many distributors. A custom gearbox, a legacy PLC module or a spindle made for one machine builder may be difficult to find at all.

Combining the 2 gives a practical matrix:

The top right cell holds most of the risk and deserves the most attention, even if those parts rarely move.

Decide how much to hold

Once you know which parts to stock, decide the quantity. The method depends on how the part is consumed.

Consumables and wear parts

Filters, belts, seals, fuses and similar items are used regularly. For these, a reorder point based on usage works well:

1. Estimate typical consumption over the replenishment period.
2. Add safety stock to cover variation in usage and supplier delays.
3. Set a minimum (the reorder point) and a maximum (the level you reorder up to).

Review these levels periodically, as consumption changes when machines are added, retired or run on different shifts.

Insurance spares

Critical parts that rarely fail, such as a main drive motor or a spindle cartridge, do not fit a usage formula. They may sit for years and then be needed urgently. The decision here is usually binary: hold 1 or hold none. Weigh the cost of the part and its storage against the cost of downtime while sourcing a replacement.

Tip: If several identical machines run in the plant, 1 insurance spare can often cover all of them. Make sure the part numbers are truly identical, including revision and firmware, before relying on that.

Plan for obsolescence

A part that is easy to buy today may be discontinued tomorrow. Manufacturers regularly announce end-of-life for drives, controllers and other electronics, and mechanical parts for older machines can disappear quietly.

Good practice includes:

• Tracking the lifecycle status of key components, especially PLCs, HMIs and servo drives
• Subscribing to manufacturer product change notifications where available
• Making a last time buy when a critical part is announced as discontinued
• Identifying alternatives early, through cross-reference or a planned upgrade (see cross-referencing part numbers)

When a part is already gone from the manufacturer's catalog, distributor stock, surplus dealers and refurbishers may still have it. A sourcing agency such as LiteHard can search that wider market on your behalf, which is often faster than calling suppliers one by one.

Keep the storeroom accurate

A strategy only works if records match reality. Typical problems are unbooked withdrawals, duplicate part numbers and wrong locations.

Practical controls:

• Use a single part number for each unique item and link manufacturer numbers to it
• Record every issue and return, even during an emergency repair
• Run cycle counts on critical and high value items rather than relying only on an annual count

Store parts so they still work when needed

A spare that has deteriorated on the shelf is not a spare. Storage conditions matter:

• Bearings: keep in original packaging, in a dry and clean area, away from vibration.
• Rubber seals and hoses: protect from heat, ozone, sunlight and solvents. Elastomers age, so follow the manufacturer's storage guidance and use older stock first.
• Electric motors: store dry. For long storage, rotating the shaft periodically helps keep bearing grease distributed.
• Electronics: use antistatic packaging and stable humidity. Some devices with electrolytic capacitors may need careful reforming before use after very long storage, so check the manufacturer's recommendations.

Label each item with part number, machines and date received.

Review the strategy regularly

Plants and suppliers change. Schedule a regular review where maintenance and purchasing look at:

• Parts that have not moved in a long time and whether they are still needed
• Stockouts that caused downtime and how to prevent them
• Upcoming obsolescence on critical equipment
• Changes in supplier reliability

This review connects the storeroom to the broader goal of reducing unplanned downtime.

Key takeaways

• Build the inventory from the asset list and maintenance history, not from what is already on the shelves.
• Classify parts by consequence of failure and difficulty of supply, and focus on parts that score high on both.
• Use reorder points for consumables and deliberate decisions for insurance spares.
• Track obsolescence actively and identify alternatives before a critical part disappears.
• Keep records accurate and store parts so they work when they are finally needed.